The present invention relates generally to a system and method for inspecting a bobbin of paper containing bands.
Systems are known in the art which unwind a first bobbin of sheet-like material (referred to as the unwind bobbin), inspect the surface of the sheet-like material, and rewind the sheet-like material onto a second bobbin (referred to as the rewind bobbin). The inspection may entail projecting electromagnetic radiation on a moving web of material. The light impinges on the surface of the moving web, where it is reflected and received at a detector device. Any anomalies in the moving web can be detected by investigating the nature of the reflected electromagnetic radiation. For instance, a tear, pinhole or blemish in the web will manifest itself in a spike in the signal level from the detector (which is attributed to an increase or decrease in reflected radiation). This spike can be viewed by connecting the detector output to an oscilloscope, as exemplified by U.S. Pat. No. 5,426,509 to Peplinkski.
The prior art rewind/inspection machines suffer a number of drawbacks. First, the prior art rewind/inspection machines are not configured to allow the operator to quickly install and remove the unwind and rewind bobbins. This is a significant factor when many bobbins must be inspected in the course of each day.
Furthermore, these machines can apply considerable tension to the web of material as it passes from the unwind bobbin to the rewind bobbin, and are therefore ill-suited for particularly fragile sheet-like material. Cigarette paper, for example, is relatively weak, making it difficult to rewind a large bobbin at high speeds without breakage. Also, cigarette paper is relatively thin, making it difficult to evenly and cleanly rewind the paper onto the rewind bobbin.
The inspection of cigarette paper presents other challenges which the prior art has not addressed. FIG. 1, for instance, shows a cigarette 360 including cigarette paper 362 containing a plurality of bands 364 formed by depositing a layer of cellulosic pulp (or other material) on the base cigarette paper 362. FIG. 2 shows a section from a bobbin of cigarette paper containing these bands. Bands formed on cigarette paper often have reflective properties similar to the cigarette paper itself. Often, for instance, the bands are formed of white colored material which is difficult to distinguish from the white colored cigarette paper. Moreover, the basis weight of a bobbin of cigarette paper may vary along the length of the paper (due to the difficulty in maintaining a constant pulp application rate during the manufacture of the paper). The variance in basis weight of the paper influences its reflective properties, thereby obfuscating the differences between banded and non-banded regions, which are subtle enough to begin with. The prior art devices do not have the ability to interpret a reflection from a web of this nature. As mentioned, these devices are configured to examine a web surface for tears, pinholes and blemishes which manifest themselves in dramatic spikes in the video camera signal.
Also, with reference to FIG. 2, the operator may be interested in determining whether the width 372 of the bands, contrast of the bands, and distance 370 between bands is within proper tolerances. Whether a band width is too long, too short, or separated from its neighboring band by more or less than a desired distance can not be determined by simply observing the properties of a single point on a moving web. Rather, the properties of a band should be gauged by determining the spatial relationship between different elements on the web. As such, the prior art which only examines local points on the web is unsuited for the task of inspecting cigarette paper containing bands.
Pattern recognition techniques are one way of determining the spatial relationship between different features on a printed web of material. In a common technique, a camera forms a digital image of a portion of a web of material and information printed thereon. The digital image is then compared with a pre-stored template representing an error-free web portion. Discrepancies between the template and the image represent an irregular web. These techniques offer accuracy, but unfortunately entail a great deal of data processing. These techniques are therefore ill-suited for the task of detecting the properties of bands on a web moving at the high speeds required in a rewinder machine.
Accordingly, it is an exemplary objective of the present invention to provide a rewind/inspection machine which does not suffer from the above noted drawbacks.